1. Field of the Invention
This invention relates generally to master cylinder and oil-hydraulic booster assemblies and more particularly to such assemblies of the type in which the booster cylinder is connected to the rear of the master cylinder and the master piston, slidably fitted in the bore of the master cylinder to produce oil-hydraulic pressure therein, and the booster piston, slidably fitted in the bore of the booster cylinder so as to be power-actuated in accordance with the input thereto, are interconnected through an output rod held in abutting engagement with the rear face of the master piston and a reaction mechanism arranged to feed the reaction force from the master cylinder back to the input side of the assembly.
2. Description of the Prior Art
Conventionally, in assemblies of the type described, the master cylinder and the booster cylinder are formed with cylindrical axial bores designed respectively to guide the master and booster pistons, differing in diameter from each other, individually over their whole length of stroking movement. Because of this, the whole length of the assembly has been very large and, for example, where the assembly is installed in an engine compartment of limited space to serve the purpose of actuating the oil-hydraulic brake system of the motor vehicle, interference with the engine and engine accessories has often made the installation practically infeasible.
In oil-hydraulic boosters, generally usable in such assembly, stop means to define the limit of retraction of the input rod thereby to determine the opening degree of the outlet valve when opened is provided solely on the booster piston and, therefore, the opening of the outlet valve remains the same not only when the booster piston is at its limit of retraction but during the whole course of its retraction.
When the input rod is driven forward for booster operation, the stroke required of the input rod to close the outlet valve and open the inlet valve is a stroke relative to the booster piston and this causes a delay in forward movement of the booster piston. It is desired, therefore, that the relative stroke of the input rod be reduced to a minimum and, to this end, the opening of the outlet valve should be limited as much as possible.
On the other hand, for rapid retraction of the booster piston from its operating position, the outlet valve opening should be set as large as possible to permit quick discharge of the hydraulic fluid from the output hydraulic chamber of the oil-hydraulic booster into the oil reservoir tank.
In this manner, the outlet valve is subject to contradictory requirements for its opening and serious considerations are required in actual design.